This invention relates to a door lock, and particularly to a door lock including a spring-loaded bolt and a main bolt which is loaded with a spring and which can be operated by using key-operated lock members provided at both inner and outer sides of a door as well as a knob provided at the inner side of the same door.
FIG. 1 shows a conventional lock 10 which includes a main bolt 11 controlled by a locking member 17 and operable by a key-operated lock member 12 which actuates an actuating member 16. The lock further includes a spring-biased auxiliary bolt 13 which is operable by a pull member 14 and which can be locked against movement when in the latching position by a locking member 19 that is operable via a control knob 18. When such a lock is used, the user may operate the main bolt from the outside of a door through the key-operated lock member 12 and operate the auxiliary bolt from the inside of the door through the pull member 14. In addition, the locking member 19 can be operated through the knob 18 from the inside of the door so as to prevent the bolt 13 from movement when the bolt 13 is in the latching position. The arrangement of the locking member 19 and the knob 18 effectively prevents a person from unlocking the door from the outside. However, this has created a disadvantage in that, if a child turns the knob at the inside of the door, thus locking the auxiliary bolt 13 against movement and no adult who can operate the knob is present, the door will be unable to be opened from the outside by operating the door lock. A situation such as this may endanger the child locked within the room.